Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

Annotations already declare readOnlyHint, idempotentHint, and destructiveHint, so the safety profile is covered. The description goes beyond annotations by disclosing that the tool charges nothing, that the data key returns 403 wrong_credential, and that a missing string returns 401 invalid_key. These operational behaviors are valuable context an agent cannot infer from annotations alone.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Is the description appropriately sized, front-loaded, and free of redundancy?

The description is dense but every clause earns its place: the returned fields are listed first, then credential requirements, then error behavior and cost. It is a single well-structured paragraph with no filler and no redundancy with the schema.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

For a read-only single-parameter tool with a full output schema, the description covers the input provenance, authentication constraints, expected error responses, and cost implications. Nothing an agent needs to call it correctly is missing.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema description coverage is 100%, so the input schema fully documents the 'secret' parameter, including its origin and precedence. The description reinforces this by repeating that the secret must come from sign_up and that the data key cannot be used, but it does not add significant new meaning beyond the schema's already detailed parameter description. Baseline 3 is appropriate.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Does the description clearly state what the tool does and how it differs from similar tools?

The description opens with a specific verb and resource: 'Reads the account behind the secret,' and enumerates exactly what the tool returns (tier, Terms version, products, credit balance, usage history, balance movements). This clearly distinguishes it from sibling tools like get_product or list_products, which focus on catalog data rather than account status.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Does the description explain when to use this tool, when not to, or what alternatives exist?

The description gives clear context on how to invoke the tool: pass the secret returned by sign_up, not the client configuration's data key. It even explains the failure modes for using the wrong credential. It does not explicitly name alternative sibling tools or state when not to use them, but the authentication guidance is strong enough to guide correct use.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.